docs: def _highlight_lines(self, tokensource):
          """
          Highlighted the lines specified in the `hl_lines` option by
          post-processing the token stream coming from `_format_lines`.
          """
          hls = self.hl_lines
  
          for i, (t, value) in enumerate(tokensource):
              if t != 1:
                  yield t, value
              if i + 1 in hls:  # i + 1 because Python indexes start at 0
                  if self.noclasses:
                      style = ''
                      if self.style.highlight_color is not None:
                          style = (' style="background-color: %s"' %
                                   (self.style.highlight_color,))
                      yield 1, '<span%s>%s</span>' % (style, value)
                  else:
                      yield 1, '<span class="hll">%s</span>' % value
              else:
                  yield 1, value